Cephalosporium stripe of wheat : seedling-based resistance screening and pathogenic variability Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9p290f78q

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  • Cephalosporium stripe of wheat (Triticum aestivum), caused by the soilborne fungus Cephalosporium gramineum, results in significant yield reductions in dryland winter wheat crops of the U.S. Pacific Northwest. The development of resistant cultivars offers the best hope for disease control. Breeding for resistance is hampered by the long trial times inherent in screening adult plants, and by cultivar x environment interactions in field tests. The principal objective of this research was to develop and test a procedure for screening wheat seedlings in controlled environments for resistance to Cephalosporium stripe. Wheat seedlings were raised hydroponically in growth chambers, and the fungus was increased in large fermentation tanks. The seedlings were inoculated at about 12 days post-germination. Disease severity was assessed approximately seven days later using a chlorophyll meter to measure the symptoms of chlorosis and striping. In three trials, five soft white cultivars from the Pacific Northwest and four hard red cultivars from the Southern Great Plains with known levels of field resistance were tested with a Pacific Northwest fungal isolate. With one exception, chlorophyll readings ordered the cultivars appropriately, with moderately resistant cultivars ranking above susceptible cultivars. Three other moderately resistant cultivars from the Pacific Northwest also appeared in one or two trials, and were ranked properly by chlorophyll level. Chlorophyll levels of uninoculated plants were assayed to determine if differences in chlorophyll content were innate in the cultivars. The chlorophyll levels of uninoculated and inoculated seedling treatments were only significantly correlated when the cultivar Madsen, which ranks high both in resistance and in chlorophyll content, was included. In adult plants, flag-leaf chlorophyll level corresponded to intensity of Cephalosporium stripe symptoms where disease was present, and was independent of known field resistance in undiseased cultivars. The seedling screening technique was used to investigate pathogenic variability in C. gramineum. In two experiments, a total of eight cultivars from the Pacific Northwest and the Southern Great Plains were tested with three fungal isolates from each region. No evidence of virulence/vertical resistance was found. There was also no significant adaptation of isolates to greater virulence on cultivars from the same region.
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